MITCHELL Starc had to overcome serious self-doubt to become the confident young quick who wants to be unleashed at Graeme Smith and his South African teammates from Thursday.

The left-armer impressed in the Adelaide nets on Tuesday with his potent mix of swing and speed, and is threatening to tip Ben Hilfenhaus out of the team for the second Test.

Starc believes he is a much better bowler than when he made a nervous debut against New Zealand in Brisbane last summer, and he has been the most physically resilient of Australia's young fast bowlers over the past 12 months.

He has also made enormous strides since addressing the self-esteem issues that threatened to hold him back when he first arrived as a scholar at Cricket Australia's Centre of Excellence.

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''I definitely did have [self-doubts]. I'd done a lot of work on that through my time at the academy,'' he said. ''I probably didn't have the greatest self-confidence but I worked through that and I'm probably better off for that now. At the academy we have sports psychologists who we have sessions with every week, so they worked for me.''

Though he will leave most of the sledging to others - ''I'm not as verbal as Patto'' [James Pattinson] - Starc said his year of shadowing the Australian team, playing the occasional Test, building his limited-overs reputation and spending a county stint with Jason Gillespie's Yorkshire had served him well.

''I feel I have improved my game and learnt so much being around the Australian team, then gone away and been left alone a bit as well, to my own devices,'' Starc said.

Ricky Ponting, who faced Starc and Hilfenhaus in the nets on Tuesday, reported that the Tasmanian had improved since lacking pace and penetration at the Gabba, where he picked up two tailend wickets.

Working in Starc's favour is that he has found his rhythm and patience through two Sheffield Shield games, taking four wickets against Victoria, and that he is a proven wicket-taker.

It won't hurt that Smith, the South African captain, has a patchy record against left-armers, having been dismissed six times by India's Zaheer Khan and five times by Mitchell Johnson.

''We haven't spoken too much about it, it's more about focusing on our game and the things we do well,'' Starc said. ''We've had a bit of time to think about new plans for Adelaide and a different track, so I'm going to treat every batsman the same, be patient and plan them out.''